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Wyszukujesz frazę "Kaprzyk, S." wg kryterium: Autor


Wyświetlanie 1-9 z 9
Tytuł:
Spin Density in Real and Momentum Space in Multi-Atom Alloys by KKR-CPA Method
Autorzy:
Kaprzyk, S.
Tematy:
71.18.+y
71.15.Cr
78.90.+t
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1953167.pdf  Link otwiera się w nowym oknie
Opis:
The application of the spin-polarized version of multiple scattering theory for obtaining electron charge and spin densities in both real and momentum spaces of concentrated, multi-atom disordered alloys is presented. This method is based on the Korringa-Kohn-Rostoker (KKR) band structure approach and coherent potential approximation (CPA) method. The effective one-electron potential is constructed within local spin density approximation. The magnetic neutron form factors are in real space of our main interest. With the recent developments of new synchrotron photon sources, the Compton profile becomes the most interesting target in momentum space. In the most of examples, spin momentum density and its specific structure due to Fermi surface will be shown. To get accurate enough description in momentum space and quantity like Compton profile, the determination of the Fermi surface must be done with high precision. In this context we show how to apply generalized Lloyd formula for accurate determination of the Fermi level. Also we show how to use efficiently complex energy integration method for the computation of matrix elements, G(r,r) or G(p,p), of the KKR-CPA Green function. Results for the iron-silicon ferromagnetic binary alloys and half-metallic ferromagnetic Heusler alloys are presented.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electronic Structure of Zinc-Blende and Hexagonal Semiconductors: Comparative Theoretical Study
Autorzy:
Konior, J.
Kaprzyk, S.
Tematy:
71.10.+x
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1932096.pdf  Link otwiera się w nowym oknie
Opis:
Using a self-consistent Korringa-Kohn-Rostoker Green function method and the local density approximation for the exchange and correlation potentials, we calculated the electronic structure and the corresponding densities of states for two semiconducting compounds that exist in both cubic (zinc-blende) and hexagonal (wurtzite and NiAs-type) crystal structures, i.e., for CdSe and MnTe. Due to the use of the same method of calculation for both structures a comparison between the obtained results and finding the factors that determine the difference between the properties of these two phases are possible. The presented local density approximation-Korringa-Kohn-Rostoker results might be of importance for the understanding of the factors that determine the relative stability of different phases of semiconducting compounds.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electronic Structure and Fermiology of High-T$\text{}_{c}$ Superconductors
Autorzy:
Bansil, A.
Kaprzyk, S.
Tematy:
71.25.-s
74.20.Mn
74.25.Jb
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1929378.pdf  Link otwiera się w nowym oknie
Opis:
We briefly discuss some of our recent results in three areas, all related to issues concerning the electronic structure and fermiology of the high-T$\text{}_{c}$'s. (i) First-principles band theory based computations of the electron-positron momentum density relevant for the interpretation of the positron annihilation (2D-ACAR) experiments; results for YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7}$ are discussed. (ii) Another k-resolved spectroscopy where such first-principles comparisons between the computed and measured spectral intensities have been crucially important is the angle-resolved photoemission experiment; we discuss results for the (001)-surface of YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7}$ where computations yield considerable insight into the nature and origin of the spectral signal associated with the CuO$\text{}_{2}$ plane bands. (iii) The study of effects of substitutions and of oxygen-vacancy disorder in the high-T$\text{}_{c}$'s; here results for the LaSrCuO$\text{}_{4}$, and Ba-K-Bi-O and Ba-Pb-Bi-O systems, with focus on the nature of the van Hove singularity in the vicinity of the Fermi energy are presented.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Formation Energy and Electronic Structure of II-VI/IV Semiconductor Superlattices
Autorzy:
Jędrzejek, C.
Konior, J.
Kaprzyk, S.
Tematy:
73.20.Dx
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1872700.pdf  Link otwiera się w nowym oknie
Opis:
We calculate formation energy and electronic structure of ultrathin (001)II-VI/IV semiconductor superlattices using the Korringa-Kohn-Rostoker all-electron method. Formation energies (∆H) are 2.18 eV for (Ge$\text{}_{2}$)$\text{}_{1}$(ZnSe)$\text{}_{1}$ and 1.50 eV for (ZnS)$\text{}_{1}$(Si$\text{}_{2}$)$\text{}_{1}$. The results of this work are significantly different from these by Ferraz and Srivastava who obtained ∆H = 0.88 eV for (001)(Ge$\text{}_{2}$)$\text{}_{1}$(ZnSe)$\text{}_{1}$ and moreover the one-layer super-lattices are metallic, which confirms the results by Ohno and Ito. The large formation energies surely lead to interfacial instability.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Interplay of Crystal Structure Preference and Magnetic Ordering in High Entropy CrCoFeNiAl Alloys
Autorzy:
Jasiewicz, K.
Kaprzyk, S.
Tobola, J.
Tematy:
71.15.Nc
71.20.Be
71.23.-k
75.50.Bb
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1030461.pdf  Link otwiera się w nowym oknie
Opis:
In this work, some relations between crystal structure and magnetic ordering in CrCoFeNiAl HEAs are discussed in view of the KKR-CPA calculations. Remarkably, it is noticed that the transition between fcc and bcc phases in the analysed CrCoFeNi_{x}Al and CrCoFeNiAl_{x} alloys is closely related to change in ordering of the local magnetic moments, namely the magnetic moment on Cr is either parallel (ferromagnetic) or antiparallel (ferrimagnetic) to the magnetic moments of other atoms (Co, Fe and Ni). On the whole, the theoretical diagram showing the fcc-bcc phase preference and their coexistence vs. alloy composition well corroborates with available experimental data.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Effect of Alloying with Ca in LaMnO$\text{}_{3}$ System Studied by KKR-CPA Method and Giant Magnetoresistance
Autorzy:
Tobola, J.
Kaprzyk, S.
Pierre, J.
Tematy:
71.20.-b
71.20.Lp
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1964825.pdf  Link otwiera się w nowym oknie
Opis:
La$\text{}_{1-x}$ Ca$\text{}_{x}$MnO$\text{}_{3}$ perovskites show semiconducting properties in the paramagnetic range. The gap is reduced near x=0.33, where ferromagnetic ordering is observed. The ferromagnetic ordering then induces a semiconductor-metal transition, and gives rise to a giant magnetoresistance effect. The ground state electronic structure calculations were done with KKR-CPA method for hypothetical cubic and ferromagnetic LaMnO$\text{}_{3}$ and CaMnO$\text{}_{3}$ compounds, as well as for disordered La$\text{}_{1-x}$Ca$\text{}_{x}$MnO$\text{}_{3}$ (x=0.33, 0.4, 0.5) alloys with real crystal data. As a result, we get a magnetic moment per formula 4.00μ$\text{}_{B}$ and 3.00μ$\text{}_{B}$ and half-metallic behaviour for end-compounds, respectively. In the ferromagnetic region a linear decrease in the magnetic moment of La$\text{}_{1-x}$Ca$\text{}_{x}$MnO$\text{}_{3}$ is observed, together with the decrease in the gap width for spin-down carriers, if doping Ca in La$\text{}_{1-x}$Ca$\text{}_{x}$MnO$\text{}_{3}$. A simple model is developed, which describes magnetic and transport properties as resulting from an exchange-induced band-crossing semiconductor-metal transition, as for instance in EuO.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Superconductivity, Weak Itinerant Ferromagnetism and Electronic Band Structure of Y$\text{}_{9}$Co$\text{}_{7}$
Autorzy:
Kołodziejczyk, A.
Wiendlocha, B.
Zalecki, R.
Toboła, J.
Kaprzyk, S.
Tematy:
74.25.Jb
74.25.Ha
74.20.Mn
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/2047310.pdf  Link otwiera się w nowym oknie
Opis:
The paper presents experimental results for the intermetallic compound Y$\text{}_{9}$Co$\text{}_{7}$ which is the first very weak itinerant ferromagnetic superconductor. The measurements of electrical resistivity, susceptibility, magnetization, specific heat, nuclear magnetic resonance, and other properties show the magnetic transition at T$\text{}_{C}$≈ 4.5 K and the onset of superconductivity at about T$\text{}_{S}$≈ 2.5 K, revealing the coexistence state within a temperature interval below T$\text{}_{S}$. A few of the results are shortly reviewed and discussed. We focus attention on our recent ultraviolet photoemission spectroscopy and their comparison with our band structure calculations. Interpretations are considered which take into account the characteristic structure of the compound and different possible types of magnetic ordering.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetoelastic Properties of MnRhAs$\text{}_{1-x}$p$\text{}_{x}$ and Band Structure Results from KKR-CPA
Autorzy:
Zach, R.
Kaprzyk, S.
Nizioł, S.
Toboła, J.
Bacmann, M.
Fruchart, D.
Wolfers, P.
Tematy:
71.20.-b
71.20.Lp
75.50.Cc
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1956499.pdf  Link otwiera się w nowym oknie
Opis:
The magnetoelastic phase transitions were observed in MnRhAs$\text{}_{1-x}$P$\text{}_{x}$ system (space group P6̅2m) by X-ray measurements (80 K < T < 300 K). For x = 0.33 and x = 0.4 contents an abrupt change of both lattice parameters and of the elementary cell volume at the metamagnetic transition was detected. The Korringa-Kohn-Rostoker electronic structure calculations performed for MnRhP compound show significant variations of densities of states at the Fermi level, while changing lattice data. The Korringa-Kohn- Rostoker-coherent potential approximation studies of disordered MnRhAs$\text{}_{1-x}$P$\text{}_{x}$ system (x=0.6, 0.8, 1.0) were done at the ferromagnetic region. From our calculations we observe moving of bands near E$\text{}_{F}$, while substituting with isoelectronic metalloid, likely as while changing the crystal data in MnRhP.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetic and Transport Properties of (Fe$\text{}_{1-x}$Ni$\text{}_{x}$)$\text{}_{2}$P in View of KKR-CPA Results
Autorzy:
Kaprzyk, S.
Nizioł, S.
Toboła, J.
Zach, R.
Bacmann, M.
Fruchart, D.
Wolfers, P.
Tematy:
71.20.-b
71.20.Lp
75.50.Cc
Pokaż więcej
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1956503.pdf  Link otwiera się w nowym oknie
Opis:
We present results of the electronic structure study for the solid solution (Fe$\text{}_{1-x}$Ni$\text{}_{x}$)$\text{}_{2}$P (space group P6̅2m). The samples were synthesized for x=0.0 up to 0.15. From the electrical conductivity measurements on these materials, it was verified that resistivity increases with increasing temperature up to the Curie point T$\text{}_{C}$ and changes the slope at T$\text{}_{C}$ decreasing when temperature is raised above T$\text{}_{C}$. To get insight into the possible origin of such observations, we carried out the Korringa-Kohn-Rostoker-coherent potential approximation electronic structure calculations for (Fe$\text{}_{1-x}$Ni$\text{}_{x}$)$\text{}_{2}$P in the range of concentration x=0.0 up to 1.0. It was found that alloying with Ni in Fe$\text{}_{2}$ P causes vanishing of spin band splitting and non-rigid band behaving of electronic valence states near the Fermi level. The polarization factor for electrons at E$\text{}_{F}$ changes in (Fe$\text{}_{1-x}$Ni$\text{}_{x}$)$\text{}_{2}$P with increasing x, and interestingly, it reaches maximum at x=0.1, closely to the concentration (x=0.08), when the largest value of T$\text{}_{C}$ and a kink in temperature dependent resistivity were detected.
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-9 z 9

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